Magnetic escapement

ABSTRACT

A magnetic escapement including a rotor driven by an external force, and escape wheel made of a magnetic material and having along its periphery radially extending magnetic teeth, said escape wheel being coupled through a coil spring to the rotor, and an oscillator having a magnetic pole piece secured at the end of one of its tines and coupled magnetically to the escape wheel teeth. The oscillator is preferably formed in a W-shape and supported at a point near its center of gravity for extension parallel to the plane of the escape wheel, and its pole piece being magnetically coupled to that tooth of the escape wheel which is farthest from the supporting point. A driving circuit of a constant output for the rotor is provided, which includes a compensating transistor and a temperature compensating element for eliminating load and temperature variations.

May 2,1972

United States Patent Sakaiet a].

Dinerstein el Sit/I16 lshikawa et a]. .5

45 66 mm MW 27 28 J 78 0 33 T N E M E P A C S E m T E N G A M m [72]Inventors: Satoshi Sakai, Hirakata; Kenzo Shiraknwa;

Norio Shimizu, both of Neyagawa. all of E i Milw K f JapanAtrorneyPierce. Scheffler & Parker Primary ABSTRACT [73] Assignee:Mlttsushita Electric Works. Limited,

Osaka, Japan [22] Filed: 0cL 27 1970 A magnetic escapement including arotor driven by an external force. and escape wheel made ofa magneticmaterial and [2i] 84,324 having along its periphery radially extendingmagnetic teeth,

Appli No.2

said escape wheel being coupled through a coil spring to the rotor, andan oscillator havin a ma netic ole iece secured [30) Foreign ApplicationPriority Dam at the end of one of its tines 5nd cofipled agnstically tothe Nov. 15 I969 escape wheel teeth. The oscillator is preferably formedin a W- Nov. [8, 1969 Nov. 2i, 1969 shape and supported at a point nearits center of gravity for exn a D. a J

tension parallel to the plane of the escape wheel, and its pole piecebeing magnetically coupled to that tooth of the escape wheel which isfarthest from the supporting point, A driving circuit ofa constantoutput for the rotor is provided, which includes a compensatingtransistor and a temperature compen- [52] US. [Si] Int.

sating element for eliminating load and temperature variations.

6 Claims, 13 Drawing Figures References Cited UNITED STATES PATENTS2946,183 7/1960 Clifford.........m.............m....74/l.5X

Patented May 2, 1972 5 Sheets-Sheet 1 EDUmG oz mo OP Pahntod Mny 2, 19723,660,737

5 Shun-Shut 2 Patented May 2, 1972 5 Shuts-Shut 5 m2; "94 08 mo @3162RESONANU FREQMNCY Patented May 2, 1972 3,660,737

5 Sheets-Sheet 4 29 fil fi --H- 0 ii i b i 5 ed;

Fig. 8 (PRIOR ART) MAGNETIC ESCAPEMENT This invention relates toimprovements in magnetic escapements used in such devices specificallyas electric clocks or the like in which a constant velocity is required.

In magnetic escapements generally, there has been suggested a type inwhich permanent magnets are secured to forward ends of a mechanicaloscillator as, for example, a tuning fork which has a specific constantfrequency, and a rotary plate made of a magnetic material, that is, aso-called escape wheel is arranged so as oppose to the permanentmagnets, said magnets being oscillated at a constant frequency by meansof the mechanical oscillator, according to which the escape wheel isrotated at a constant speed. In the above arrangement, however, there isa drawback, because, since the magnet and rotary plate are coupled onlymagnetically, the rotation of the rotary plate is apt to become unstablebecause of shocks or the like given externally, wherebymis-synchronizing or even interrupting the rotation of the plate will becaused. The present invention removes the above defect of conventionalescapements.

According to the present invention, the above mentioned defect isremoved with an arrangement by which the escape wheel and driving shaftof the wheel are coupled by a spring having a low rigidity. That is, theexternal shocks are effectively absorbed by the resiliency of saidspring and any deviation from the normal relative position of theoscillator to the escape wheel is also damped by the resiliency of thespring, whereby the defect that the magnetic couple is readily broken iseffectively avoided.

A main object of the present invention is therefore to provide animproved magnetic escapement which is stable against any external shocksand produces constant rotation at uniform speed, causing less likelihoodof mis-synchronization.

Another object of the present invention is to provide a magneticescapement having a large exciting force and may be made in compactform.

A further object of the present invention is to provide a magneticescapement which is capable of adjusting the speed of the escape wheel.

Other objects and advantages of the present invention will be madeapparent as the following detailed disclosures proceed with reference tothe accompanying drawings, in which:

FIG. 1 is a perspective view of the magnetic escapement according to thepresent invention.

FIG. 1B shows a circuitry diagram ofa driving circuit for theescapement.

FIG. 2 is a plan view showing partly in section the main part of theescapement in FIG. 1.

FIG. 3 is a vertical view showing partly in section the main part inFIG. 2.

FIG. 4 is a vertical section of escape wheel unit showing details of thesame.

FIG. 5 is a diagram showing resonance curve of the oscillator used inthe present invention.

FIGS. 6 8 are circuitry diagrams of conventional driving circuits forthe magnetic escapement.

FIGS. 9 and 10 show diagrammatically voltage-current characteristics atthe collector and base of the transistor used in the driving circuit,respectively.

FIG. 11 is a diagram showing voltage characteristics.

FIG. 12 is a diagram showing output variations with respect totemperatures.

While the present invention shall be disclosed in detail with referenceto a preferable embodiment, it should be understood that the trueintention is not to limit the invention to the particular embodiment asillustrated, but is rather to cover all possible alterations,modifications and equivalent arrangements which are included in thescope of the invention as defined in the appended claims.

Referring now to FIG. 1, l is an oscillator or oscillating governer,which is formed substantially in a W-shape as shown in FIG. 3 and isfixed to a supporting member 8 at the center of gravity, shown at 17, ofthe oscillator l. The supporting member 8 is secured to a fixed base 16by means of screws [8, and said base 16 in turn is secured to a frameplate l5. 9 is a dead weight secured to a free end of the supportingmember 8. The oscillator 1 is provided with a permanent magnet 2 and abalance weight 2' made of a magnetic material, respectively secured toeach free end of the oscillator I.

3 is an escape wheel, of which details are shown in FIG. 4. That is, theescape wheel 3 is secured to a boss 7, which is fixed to a driving shaft6. 4 is a rotor consisting of a cylindrical permanent magnet in which Nand S poles are alternately arranged along its peripheral surface. Saidrotor 4 is fixed around a sleeve 12 which is mounted over the drivingshaft 6 for free rotation therearound. The sleeve 12 is provided adjacent the lower end with a threaded part 12' for starting the rotor. 13is a driving gear secured to the shaft 6 and the sleeve 12 rests on theupper surface ofthe gear 13. I1 is a coil spring, which is fixed at anend to the escape wheel 3 and at the other end to the rotor 4. 22 is aworm gear fixed on the shaft 6.

Referring again to F IG. 1, means for supporting the driving shaft 6 isprovided in the form of a pair of pedestal plates 14 and 14',respectively formed by bending a part of the frame plate 15 at rightangles thereto, so as to support the shaft 6 between said plates 14 and14' for free rotation. A further frame plate 20 is arranged in parallelrelation to the frame plate 15 and is secured thereto by means of screwsthrough spacers 19. The worm 22 is in mesh with a gear wheel 23, whichin turn is in mesh with a gear 24, so that the escapement is connectedto a gear system for driving hour-hand, minutehand and secondhand. Sis acoil assembly including a driving coil for the rotor 4 and a detectingcoil. The coil assembly 5 is mounted to the frame plate 15 by means ofscrews 26 through an insulating board 25. A speed adjusting member 34made of a magnetic material is provided adjacent the permanent magnet 2mounted on the tine of the oscillator I. The member 34 is fixed on anadjusting screw 35, which is screwed at one end into a threaded hole ofthe frame plate 15 so that the position of the speed adjusting member 34will be varied by turning the screw 35, thereby influencing the specificfrequency of the oscillator I so as to vary it and consequently thenumber of rotation of the escape wheel 3.

The escape wheel 3 is made of a magnetic material and is provided withradial magnetic teeth 36 at regular intervals. The oscillator 1 issupported by means of the fixed base 16, so that its longitudinal axiswill be parallel to the plane of the escape wheel 3 and the permanentmagnet 2 secured to one of the tines of the oscillator 1 will bedisposed above the escape wheel 3 so as to oppose that tooth 36 of thewheel 3 which is remote from the fixed base 16. 21 is a manual drivinglever provided for kicking the threaded part 12' of the sleeve 12 andthe driving gear l3 simultaneously so that the driving shaft 6 and rotor4 will be started in the desired direction.

According to the present invention, as referred to in the foregoing, theoscillating governor or oscillator l is supported by the supportingmember 8 which has the dead weight 9. This dead weight 9 is provided forthe purpose of reducing the amplitude of unnecessary oscillations of theoscillator 1, so that the accuracy of the oscillator is very high. Thatis, as diagrammatically shown in FIG. 3, in the case when the both tinesof the oscillator are oscillated in the same phase, that is, in theasymmetrical mode at a lower specific frequency f, the oscillationamplitude is relatively smaller than in the case of the reverse phase orsymmetrical mode oscillation at a higher specific frequency f,. It meansthat the resonance sharpness value at the frequency f, is low and theoscillator is unable to accomplish higher accuracy while it oscillatesat this frequency. Further, when the oscillation frequency is low, suchas f, the output of the rotor rotating at the speed corresponding tothis frequency f 1 is insufficient and hence the motor is no longerrotatable and, consequently, the synchronized rotation of the wheel 3 isno longer established. In order to prevent such inadequate oscillationof the oscillator in the asymmetrical mode at the lower frequency f,therefore, the weight 9 having a suitable weight for absorbing suchoscillation of the frequency f, is provided at the opposite end of thesupporting member 8 to a connecting part 8' with respect to thesupporting point I7. Thus. the oscillator 1 according to the presentinvention can be oscillated always in the symmetrical mode at the higherfrequency f, and, therefore, a highly accurate and synchronized rotationof the escape wheel 3 can be accomplished.

Turning now to FIG. 1B. an electric circuit for controlling the coilassembly 5 in the magnetic escapement of FIG. 1 is shown. In thedrawing, 27 is a detecting coil and 28 is a driving coil. These twocoils 27 and 28 are wound as stacked so as to form the coil assembly 5.29 is a PNP type transistor, 30 is a compensating NPN type transistor.3l is a condenser for preventing parastic oscillation, 32 is a DCsource. and 33 is a temperature compensating element. An end a of thedetecting coil 27 is connected to the base of the transistor 29 and theother end I: is connected to an end of the driving coil 28 and also tothe emitter of the transistor 29. The other end d of the driving coil 28is connected to the collector of of the compensating transistor 30. Thebase of the transistor 29 and the emitter of the transistor 30 areconnected to each other through the temperature compensating element 33.and between the collector of the transistor 29 and the collector of thetransistor 30 the DC. source 32 is inserted. The condenser 31 isinserted between the base and collector of the transistor 29.

The operation of the device according to the present invention shall nowbe explained.

When the manual driving lever 21 is operated under the condition inwhich the direct electric current is supplied to the coil assembly 5,the driving shaft 6 and the permanent magnet rotor 4 are started in afixed rotating direction, so that the rotor 4 begins to rotate. Sincethe escape wheel 3 is coupled to the rotor 4 through the coil spring 11,the rotation of the rotor 4 is transmitted to the wheel 3 and thus thewheel 3 is also caused to rotate together with the rotor. As the escapewheel 3 is thus rotated, the oscillator I carrying at a tine thereof thepermanent magnet 2 which is magnetically coupled to the magnetic teethof the wheel is excited by the teeth each time a tooth passes beneaththe magnet 2. Here, at the time when the frequency of this excitationcoincides with the specific frequency of the oscillator 1. theoscillator 1 will be in its resonant state. The escape wheel 3 isrestricted, at this time, to a speed conforming with the specificfrequency of the oscillator I.

As described in the foregoing, the speed adjusting member 34 made of amagnetic material is mounted on a movable screw 35 in the oscillatingdirection of the oscillator I, so that the member 34 is located at aposition opposite to one of the poles of the permanent magnet 2 inattractive relation to the latter and is movable together with the screw35. If the speed adjusting member 34 is moved so as to vary theattracting force acting between the member 34 and magnet 2. the specificfrequency of the oscillator l is caused to vary. Therefore, it ispossible to adjust the number of revolutions per unit time period of theescape wheel 3.

FIGS. 6. 7 and 8 show conventional driving circuits. In the circuitshown in FIG. 6. the detecting coil 27 is inserted between the base andthe emitter of the transistor 29, the DC. source 32 and driving coil 28are connected in series between the collector and the emitter of thetransistor 29, and the parastic oscillation preventing condenser 31 isconnected between the base and the collector of the transistor 29. Inthe circuit of FIG. 7, an NPN type transistor is used for the transistor29, and a DC. blocking condenser 36 and a bias resistance 37 are used.These elements cause, however, the circuitry output to be varieddepending on variations in the prevailing conditions such astemperature. source voltage and the like and, in the case when these areused for the transistor motor, its drive is unstable due to the relationof the torque and load That is, when the temperature is varied andreaches a high temperature. the base voltage V, base current I,

characteristics are transferred as shown by the broken line in FIG. 10.and the base current is increased from i to i Due to this increase. thecollector voltage is varied from i to i in the collector voltage Vcollector current I characteristics shown in FIG. 9. and consequentlythe circuitry output is increased. If the voltage is decreased, on theother hand. in the case when a biasing circuit is accompanied or thetransistor is made to operate close to its saturation point. the voltageis varied from E. to E, and the collector current is varied from i to iin the V l characteristics of FIG. 9, so that the circuitry output isdecreased. Further, in the case when the transistor is unsaturated, evena slight variation of the base current will influence the output. Inorder to prevent this, there has been suggested such a circuit as shownin FIG. 8. in which a diode 38 is connected between an end of thedriving coil 28 and the base of the transistor 29. However. this circuithas such inconveniencies that its compensation is insufficient and thetemperature characteristics are dependent upon the transistor 29 anddiode 38. According to the present inven tion. the above describeddefects of the conventional driving circuits can be overcome.

In the driving circuit according to the present invention, for thepurpose of making the base current of the transistor 29 constant at alltimes, the compensating current i, is determined by the voltage V acrossbase and emitter and the resistance value of the temperaturecompensating element 33.

The state of the compensation shall be explained now in detail. When theprevailing temperature rises. the V, I, characteristics of thetransistor are changed to the state of the broken line shown in FIG. 10and the base current is increased from i to i In order to reduce thisincreased base current of the transistor 29, it may be sufficient toincrease the compensating current i Since, on the other hand, the basecurrent at the compensating transistor 30 is also increased, thecompensating current i is also made to be increased so as to make thebase current of the transistor 29 constant. It is possible to furthercompensate for possible differences between the respectivecharacteristics of the transistors 29 and 30. That is, for thetemperature compensating element 33, either type of such element havingpositive or negative temperature coefficient is used depending on therequirement. In the case when the load of the motor or the like isreduced, the motor speed is increased and the induction voltage of thedetecting coil 27 is increased, so that the base current i is increased.On the other hand. the respective terminal voltages e, and e of thedetecting coil 27 and driving coil 28 are increased. Due to theseincreases. the emitter-base voltage V of the compensating transistor 30is also increased, so that the compensating cur rent i, is made toincrease so that the base current i of the transistor 29 is notincreased and, thus, the motor speed can be kept at a constant rate.

The above described effects shall be explained with reference to theembodiment. In the voltage characteristic diagram of FIG. II. the solidline curve shows the case of the present invention and the broken linecurve shows the conventional case. As is clear from the curves, anexcellent result has been obtained according to the present invention.The diagram shown in FIG. 12 shows output variations due to thetemperature, in which the broken line curve shows the case where nocompensating means is used.

Next, the features of the present invention shall be explained.

A. As has been described in the foregoing, according to the presentinvention, the driving shaft 6 and the escape wheel 3 are coupled bymeans of the coil spring I] which is low in rigidity and, therefore. anyshocks given from outside the device are softened (or absorbed) by theresiliency of the coil spring, so that no large influence will beexerted upon the magnetic coupling of the escape wheel to theoscillator.

B. The oscillator is arranged in such manner that its longitudinal axiswill be parallel to the plane of escape wheel and that at least one ofits forward ends will be positioned adjacent the tooth of the escapewheel which is remote from the supporting point of the oscillator.Therefore, it is possible to make the dimension of the magneticescapement smaller than in the conventional cases so that the forwardend or ends of the oscillator will be positioned substantially at thecenter of the escape wheel or near the supporting point of theoscillator,

C. As the oscillator l is formed substantially in a W-shape andsupported at the point 17 which is close to the center of gravity anyshocks given to the oscillator through the frames 15, 20 will betransmitted always near the center of gravity of the oscillator 1.Therefore, it is practically impossible that the moment due to the shockwill be reproduced in the oscillator and, thus, the oscillator l is lessinfluenced by the shock.

D. In the driving circuit, the compensating transistor is inserted insuch manner that its base and collector are connected to theintermediate tap and collector side terminal of the driving coil,respectively, and the emitter of this transistor is connected throughthe temperature compensating element to the base of the transistor.Therefore, any variations in the prevailing temperature will becompensated for by the temperature characteristics of the compensatingtransistor and temperature compensating element, and any variations inthe load will be compen sated for by the compensating transistor with adetection of the voltage at the detecting coil and driving coil, wherebythe output of the driving circuit may always be stable.

What is claimed is:

l. A magnetic escapement comprising a rotor, means providing a force forrotating said rotor, an escape wheel, a coil spring for coupling saidescape wheel to said rotor, said escape wheel being formed of a magneticmaterial and having a plurality of magnetic teeth extending radiallyfrom the peripherey thereof at regular intervals, an oscillatorextending in a direction parallel to said escape wheel, means forsupporting said oscillator, and a permanent magnet at one only of theforward ends of said oscillator for oscillation in a direction parallelto the plane of the escape wheel.

2. A magnetic escapement as claimed in claim I wherein said permanentmagnet is secured to said one forward end of said oscillator opposed tothe magnetic tooth of the escape wheel which is remote from the point ofsupport of the oscillator.

3. A magnetic escapement as claimed in claim 1 wherein said oscillatoris formed substantially in a W-shape and is supported by said supportmeans at a position near its center of gravity.

4. A magnetic escapement as claimed in claim 1 wherein said oscillatoris formed substantially in a Wshape and is supported by said supportmeans at a position near its center of gravity, and further comprising aweight attached to the other of said forward ends of said oscillator,said weight being suffi cient to absorb the specific frequencycorresponding to the frequency in the asymetrical mode.

5. A magnetic escapement as claimed in claim I wherein said permanentmagnet is provided with a magnetic pole at each end thereof, one of saidpoles being opposed to the magnetic force of the said escape wheel andfurther comprising means for adjusting the speed of oscillation of saidoscillator made of a magnetic material and movable in the oscillatingdirection of said oscillator, the other of the poles of said permanentmagnet being opposed to the magnetic force of said adjusting means.

6. A magnetic escapement as claimed in claim 1 wherein said means forrotating said rotor comprises a rotor driving circuit including a firsttransistor, a detecting coil connected between the emitter and base ofsaid first transistor, a driving coil connected in series with saiddetecting coil for exciting said rotor and connected between the emitterand collector of said first transistor through a source of current, thejunction point of said detecting coil and driving coil being connectedto the emitter of said irst transistor, a second compensating

1. A magnetic escapement comprising a rotor, means providing a force forrotating said rotor, an escape wheel, a coil spring for coupling saidescape wheel to said rotor, said escape wheel being formed of a magneticmaterial and having a plurality of magnetic teeth extending radiallyfrom the peripherey thereof at regular intervals, an oscillatorextending in a direction parallel to said escape wheel, means forsupporting said oscillator, and a permanent magnet at one only of theforward ends of said oscillator for oscillation in a direction parallelto the plane of the escape wheel.
 2. A magnetic escapement as claimed inclaim 1 wherein said permanent magnet is secured to said one forward endof said oscillator opposed to the magnetic tooth of the escape wheelwhich is remote from the point of support of the oscillator.
 3. Amagnetic escapement as claimed in claim 1 wherein said oscillator isformed substantially in a W-shape and is supported by said support meansat a position near its center of gravity.
 4. A magnetic escapement asclaimed in claim 1 wherein said oscillator is formed substantially in aW-shape and is supported by said support means at a position near itscenter of gravity, and further comprising a weight attached to the otherof said forward ends of said oscillator, said weight being sufficient toabsorb the specific frequency corresponding to the frequency in theasymetrical mode.
 5. A magnetic escapement as claimed in claim 1 whereinsaid permanent magnet is provided with a magnetic pole at each endthereof, one of said poles being opposed to the magnetic force of thesaid escape wheel and further comprising means for adjusting the speedof oscillation of said oscillator made of a magnetic material andmovable in the oscillating direction of said oscillator, the other ofthe poles of said permanent magnet being opposed to the magnetic forceof said adjusting means.
 6. A magnetic escapement as claimed in claim 1wherein said means for rotating said rotor comprises a rotor drivingcircuit including a first transistor, a detecting coil connected betweenthe emitter and base of said first transistor, a driving coil connectedin series with said detecting coil for exciting said rotor and connectedbetween the emitter and collector of said first transistor through asource of current, the junction point of said detecting coil and drivingcoil being connected to the emitter of said first transistor, a secondcompensating transistor having the base connected to an intermediate tapon said driving coil and the collector connected to an end terminal ofsaid driving coil, and a temperature compensating element insertedbetween the emitter of said second compensating transistor and the baseof said first transistor.